Compositions comprising an epoxy resin, dicyaniamide and an acylguanidine

ABSTRACT

Mixtures storable at room temperature for periods up to 30 days, yet which cure quickly at moderately elevated temperatures and are suitable for the manufacture of shaped structures, coatings and adhesive bonds, have been prepared comprising an epoxy resin, dicyaniamide as a curing agent, and an acylguanidine as an accelerator for the cure.

Son et al.

COMPOSITIONS COMPRISING AN EPOXY RESIN, DICYANIAMIDE AND ANACYLGUANIDINE Inventors: Pyong-Nae Son, Akron; Carl D.

Weber, Copley, both of Ohio Assignee: The B. F. Goodrich'Company, New

York, N.Y.

Filed: Nov. 1, 1971 Appl. No.: 194,524

[56] References Cited UNITED STATES PATENTS 3,397,156 8/1968 Lopez etal. 260/47 X 3,391,113 7/1968 Lopez et a1 ..260/47 PrimaryExaminerWilliam H. Short Assistant ExaminerT. Pertilla Attorney-AlbertC. Doxsey et a1.

[57] ABSTRACT Mixtures storable at room temperature for periods up to 30days, yet which cure quickly at moderately elevated temperatures and aresuitable for the manufacture of shaped structures, coatings and adhesivebonds, have been prepared comprising an epoxy resin, dicyaniamide as acuring agent, and an acylguanidine as an accelerator for the cure.

5 Claims, N0 Drawings BACKGROUND OF THE INVENTION Epoxy resins have beencured with dicyandiamide and similar materials at elevated temperaturesto form insoluble, crosslinked, high molecular weight products. Thecured products have good chemical and mechanical properties includingexcellent adhesion to metals and many other materials. Mixtures of epoxyresins and dicyandiamide store well at room temperature and are usefulin molding compositions.

An amount of from 3 to parts of curing agent per 100 parts resin isgenerally capable of crosslinking epoxy resins at a temperature of 175C. 250 C. in about 45 to 60. A preferred curing agent is cyanoguanidine(dicyandiamide). This material is representative of useful curing agentsof the class which is represented by the formula:

wherein R R R and R are the same or different and are selected from thegroup consisting of hydrogen, cyano, C, to C alkyl groups, and C to Chydroxyalkyl groups. The correspon ing bis compounds, such as biguanide(NI-l CNI-l NH CNl-l NH and heptamethylisobisguanide may also be used.

For many applications the epoxy resin systems cured with dicyandiamidealone have undesirably long curing times at relatively high temperaturesand it would be useful to have epoxy resin compositions that will storewell at room temperature, yetcure readily to a thermoset condition atrelatively low temperatures in a short period of time, for example, inless than 60 minutes at 120 C. or in less than 30 minutes at 150 C. Hightemperature cures are undesirable because of the expense involved inobtaining them. In addition the high temperatures often cause yellowingin certain stocks and may otherwise adversely affect properties of oneor more parts of a composition being cured.

Conventional accelerator additives for cure of epoxy resins includepolycarboxylic acid anhydrides. These cure systems are also known to beaccelerated by the addition of tertiary amines. When tertiary amines areemployed to accelerate a dicyandiamide cure of epoxy resin, only minorimprovement is obtained. If the amount of tertiary amine accelerator isincreased sufficiently to satisfactorily accelerate the dicyandiamidecure, storage properties of the composition are found to be impaired.

Dicyandiamide is an effective curing agent for epoxy resins andcombinations of epoxy resin anddicyandiamide have good room temperatureaging characteristics. It is desirable to find'an additive for the epoxyresin-dicyandiamide cure system that will not significantly detract fromthe room temperature storability of the composition, yet will acceleratethe final cure so that shorter times, in the range l0 to 30', and/orlower SUMMARY OF THE INVENTION It has been discovered thatl,l,3,3-tetraalkyl-2-acylguanidines have high activity as acceleratorsfor cure of epoxy resins with dicyandiamide. In the ranges in which theyact as accelerators for cure of epoxy resin with dicyandiamide, many ofthese substituted guanidines have little or no adverse effect on thestorability of I epoxy resin-dicyandiamide mixtures or on the propertiesof the cured products. Stability varies somewhat depending upon the typeand concentration of substituted guanidine used. The mixtures can bestored at room temperature for up to about 30 days.

This invention provides storable mixtures which cure quickly atmoderately elevated temperatures and are suitable for the manufacture ofshaped structures, coatings and adhesive bonds. The compositions areespecially useful in the forms of powdered or granulated materialscontaining a) a polyepoxy compound whose molecule contains an average ofmore than one epoxide group, b) dicyandiamide as a curing agent and c)as a curing accelerator a 2-acyl substituted guanidine of the formula inwhich R represents an aromatic group of six to l0 carbon atoms,hydrogen, or an alkyl group of one to four carbon atoms. When R is anaromatic group, said group may bear substitution such as chloro or nitroin the 0-, m-, or ppositionYThe terms R, and R are alkyl groups of oneto five carbon atoms. They may be the same or different, but, preferablyare both methyl.

The term n is a number from I to 15. The Z-acyl substituted guanidinesof this invention are readily prepared by the reaction of acyl chloridesoralkanesulfonyl chlorides with tetraalkylguanidine in the presence of atertiary amine catalyst such as triethylamine. Tetraalkylguanidines suchas tetramethylguanidine are commercially available.

An advantage of these 2-acyl substituted guanidines as accelerators fordicyandiamide cure of epoxy resins is that they disperse readily andhomogenously into a mixture of epoxy resin and dicyandiamide. The effectof these accelerators is evident when they are employed in an amount aslow as 0.05 part by weight per lOO parts of epoxy resin. As high as 10parts accelerator can be employed. More than this amount of acceleratorleads to a dropoff in room temperature storage life of the mixtures. Thepreferred range of accelerator is 0.l to 2.0 parts per 100 parts epoxyresin.

temperatures, in the range C can be employed to accomplish the cure.

The preferred range of curing agent (preferably dicyandiamide) employedin this process is 5 to 15 parts per 100 parts of epoxy resin.

The term "polyepoxide resin as used herein describes the polymericreaction products of polyfunctional halohydrins such as epihalohydrinswith polyfunctional hydrogen-donating reactants, or their salts, such aspolyfunctional phenols, alcohols, amines, acids and their salts. Themajor reaction is presumably a splitting out of hydrogen or metal haliewith simultaneous opening and reaction of the epoxy ring. The resinmolecule would then contain functional hydroxy side groups, 1.2 epoxyend groups, and ethereal or ester linkages. A small proportion ofhydroxy end groups are also likely to be present. Other terms often usedsynonomously with polyepoxide resin are polymeric glycidyl ethers andepoxy-hydroxy polyether resins. The term polyepoxide resin as usedherein is also intended to include glycidyl polyesters as well asglycidyl polyethers. The important common properties are the resinouscharacter and the functional 1.2 epoxy and hydroxy groups. Polyepoxideresins are also preparable from epoxy containing compounds having anon-halide, hydrogen bonding reaction group.

A typical method of preparing a polyepoxide resin is described in U.S.Pat. No. 2,500,449 in which epichlorohydrin is reacted with bisphenol at100 C. in the presence of sufficient alkali to bind the hydrochloricacid formed. The resins formed vary according to the molar proportionsand reaction conditions, and have melting points ranging from 43 to 1 12C. In this particular case the end groups are presumed to be epoxygroups while there are many intermediate functional hydroxy groups.Further hardening of a typical polyepoxide resin such as this isprovided by heating with a hardening agent, usually bi-functional, whichacts to cross-link the previously formed resin, e.g. oxalic acid, citricacid, inorganic bases, organic bases etc. Other polyepoxide resins andmethods are described in U. S. Pat. Nos. 2,444,333; 2,528,932;2,500,600; 2,467,171 and others.

Polyepoxide resins are available commercially in a wide range of epoxycontent, molecular weight, softening point and composition. Epoxyresins, containing an average of at least one epoxide group per moleculeunit in the formula, include polymers produced by condensation ofepichlorohydrin with bisphenol A, alicyclic polyepoxides such asepoxyethyl-3,4-epoxycyclohexane (vinylcyclohexene diepoxide),dicyclopentadiene diepoxide, 3 ,9-bis( 3 ,4'-epoxycyclohexyl )-spirobi(meta-dioxane); dior polyglycidyl ethers of polyhydric alcohols such as1,4 butanediol or of polyglycols such as polypropylene glycols; diorpolyglycidyl ethers of polyhydric phenols such as resorcinol,bis(p-hydroxyphenyl) methane, 2,2-bis(phydroxyphenyl) propane,l,l,2,2-tetrakis (p-hydroxyphenyl) ethane; condensed products of phenolsreacted with formaldehyde under acid conditions such as phenol-novolaks,and the like.

These mixtures of epoxy resin, dicyandiamide and 2- acylguanidines arereadily cured at 100 C to 150 C in from 2 to 30 minutes with to 30minutes being preferred. When the cure is extremely rapid at the lowertemperatures, the compositions often are difficult to handle and processsuccessfully.

The term curing" as used herein means the conver sion of soluble liquidor fusible polyepoxide into solid, infusible, insoluble threedimensionally crosslinked material. The cure may be accompanied bycasting, molding or other shaping technique. Coatings and adhesives inthe form of films may be formed before the cure is completed.

The curable mixtures of this invention may further contain plasticizerssuch as dioctyl phthalate, inert solvents such as styrene oxide,extenders, fillers or reinforcing agents. Typical of the lattermaterials that can be employed are bitumen, textile fiber glass fibers,mica, titanium dioxide, kaolin, carbon black and various dyestuffs.

The curable epoxy resin, curing agent, accelerator mixtures of thisinvention are evaluated by a test for measuring gel time by thefollowing internal testing method:

Resin, curing agent, and accelerator are mixed in a test tube andstirred while being heated to the selected reaction temperature in aconstant temperature bath. Once triggered, the reaction is exothermicand produces a peak exotherm higher than the bath temperature. Testbatches total about 5 grams of material. A thermocouple probe, connectedto a temperature recorder, is inserted in the batch. The batch isstirred slightly every 30 seconds with the temperature probe. Time toreach reaction temperature and then the time to reach peak exotherm areindicated on the recorder chart. Actual solidification of the batchgenerally takes place just before the peak exotherm is recorded, butinitial solidification is a condition that is difficult to determinevisually. The time to raise the temperature from room temperature to thepeak exotherm is therefore taken as the gel time of the sample batch.

DETAILED DESCRIPTION OF THE INVENTION Preparation of l,l,3,3-TetramethylGuanidine Derivatives l ,1 ,3,3-tetramethyl-2-benzoyl guanidineTetramethyl guanidine (Eastman Kodak Co.), 57.6 g. (0.5 mole), and 50.6g. (0.5 mole) triethylamine dissolved in 400 ml tetrahydrofuran areplaced in a dry 2 liter flask. The solution is cooled to 9 C. and 70.3g. 0.5 mole) of benzoyl chloride in 200 ml. tetrahydrofuran is addeddropwise. A white precipitate of triethyl ammonium chloride forms.Temperature is maintained at 9 18 C. The slurry is stirred two hours,then filtered. The precipitate is washed with tetrahydrofuran and thecombined washings and filtrate are concentrated on a rotary evaporatorto form a yellow syrup in the amount of l 10 g. (86 percent of theory).

The yellow syrup analyzes as l,l,3,3-tetramethyl-2- benzoyl guanidine byelemental analysis, infrared, mass spectroscopy and nuclear magneticresonance (NMR).

Analysis: calculated for C I-I N 0, C, 65.72; H,

7.82; N, 19.17. Found C, 65.36; H, 7.77; N, 19.49.

Using the same procedure and varying the acyl chloride as shown in Table1 below gives the substituted tetramethyl guanidines listed in Table 1.

TABLE 1 (Acyl) chloride 1,1,3,3 tetramethyl Designaguanidine tionBenzoyl chloride 1 ,1 ,3,3,-tetramethyl- 2-benzoyl quanidine A Acetylchloride 1,1 ,3,3-tetramethyl- 2-acetyl guanidine B Phenylmethane l, 1,3,3-tetramethylsulfonyl Z-phenylmethane sulfonyl F chloride guanidineEXAMPLE 1 An epoxy resin of diglycidyl ether of bisphenol A andepichlorohydrin having an avg. mol. wt. of 360-390 (Epon 828) is curedwith dicyandiamide and 1,1,3,3- tetramethyl-2-acetyl guanidine (B) bymixing the ingredients in the proportions shown below and heating in aconstant temperature bath gel test described above.

TABLE 2 Material Parts by weight Epoxy resin 100 Dicyandiamide 121,1,3,3-tetramethy1-2- 4 acetyl guanidine Temp. of Gelation Time of Gel100C 29 min. 120C 8 min. 10 sec.

EXAMPLE 2 The Z-acyl substituted guanidines prepared and identifiedabove are evaluated in the gel test procedure at a bath temperature of121 C. The test sample contains 100 parts Epon 828 resin, 12 partsdicyandiamide and 4 parts accelerator. With each accelerator material, acontrol is run omitting the dicyandiamide to determine if the acylsubstituted guanidine contributes When the accelerator employed is 4parts methane sulfonyl chloride and 4 parts phenylmethanesulfonylchloride, equivalent cure results are obtained.

The materials of the invention do not contribute sig nificantly to cureunless dicyandiamide is present as the curative. The accelerators enableone to cure an epoxy resin-dicyandiamide appreciably faster and at anappreciably lower temperature than when the accelerators are absent.Tetramethyl guanidine, the parent compound of the2-acyl-tetramethylguanidines, gives too fast a cure. The products of toofast cure tend to be poor in adhesion and processing of the adhesivecomposition is difficult.

EXAMPLE 3 Epoxy resin, parts) dicyandiamide (12 parts) and a range ofaccelerator are evaluated in the gel test procedure at 121 C bathtemperatures with these results:

TABLE 4 2-Acety1-1,1,3,3- tetramethyl guanidine parts 1 2.6 5 Time togel minutes 15' 1025" 7'30" Peak Exotherm (C) 198 We claim:

l. A curable composition consisting of 100 parts polyepoxide resincontaining an average of more than one 1.2-epoxide group per molecule,from 3 to 15 parts by weight of dicyandiamide curing agent, and from0.05 to 10.0 parts by weight of a curing accelerator of the formula inwhich R represents an aromatic group of six to 10 carbon atoms,hydrogen, or an alkyl group of one to four carbon atoms, R and R arealkyl groups of one to five carbon atoms and may be the same ordifferent, n is a number from 1 to 15 said composition beingcharacterized by the ability to cure in 8' to 30' when heated to 100 150C.

2. A composition as claimed in claim 1 in which the said accelerator is1,1,3,3-tetramethyl-2-benzoyl guanidine.

3. A composition as claimed in claim 1 in which the said accelerator isl,l,3,3-tetramethyl-2-acetyl guanidine.

4. A composition as claimed in claim 1 in which the said accelerator is1,1 ,3,3-tetramethyl-2-(pnitrobenzoyl) guanidine.

5. A composition as claimed in claim 1 in which the said accelerator isl l ,3,3-tetramethyl-2-(pchlorobenzoyl)guanidine.

2. A composition as claimed in claim 1 in which the said accelerator is1,1,3,3-tetramethyl-2-benzoyl guanidine.
 3. A composition as claimed inclaim 1 in which the said accelerator is 1,1,3,3-tetramethyl-2-acetylguanidine.
 4. A composition as claimed in claim 1 in which the saidaccelerator is 1,1,3,3-tetramethyl-2-(p-nitrobenzoyl) guanidine.
 5. Acomposition as claimed in claim 1 in which the said accelerator is1,1,3,3-tetramethyl-2-(p-chlorobenzoyl)guanidine.